qpid: ensure supported exchange types are declared (#1034)

This is a follow-up to ddba8aeaf0. Prior to that commit,
"implements" was missing entirely for qpid. The earlier commit
added it, but only declared that the transport was async-capable.

Turns out it's important also to declare the supported exchange
types. In particular, if the transport doesn't declare support
for the 'fanout' exchange type, pidbox wouldn't be used[1] and so
it would still not be possible to revoke a task with terminate=True
when using the qpid transport.

[1] https://github.com/celery/celery/commit/2f58c35340f648

kombu/transport/qpid.py

@@ -1408,6 +1408,7 @@ class Transport(base.Transport):
     # This Transport does support the Celery asynchronous event model.
     implements = virtual.Transport.implements.extend(
         asynchronous=True,
+        exchange_type=frozenset(['direct', 'topic', 'fanout']),
     )
 
     # The driver type and name for identification purposes.

t/unit/transport/test_qpid.py

@@ -1667,6 +1667,12 @@ class test_Transport_class_attributes(object):
         assert Transport.driver_type == 'qpid'
         assert Transport.driver_name == 'qpid'
 
+    def test_verify_implements_exchange_types(self):
+        assert 'fanout' in Transport.implements.exchange_type
+        assert 'direct' in Transport.implements.exchange_type
+        assert 'topic' in Transport.implements.exchange_type
+        assert 'frobnitz' not in Transport.implements.exchange_type
+
     def test_transport_verify_recoverable_connection_errors(self):
         connection_errors = Transport.recoverable_connection_errors
         assert ConnectionError in connection_errors